A holding arrangement of the above type is disclosed in U.S. Pat. No. 6,963,444. There, a stand arrangement for a medical-optical instrument is described. In this stand arrangement, the medical-optical equipment is held on a front arm which is coupled via a rack and pinion gear assembly to an electric motor. The holding arrangement includes a vibration sensor with a control loop. This control loop makes it possible to control the electric motor so that vibrations of the medical-optical equipment on the front arm are actively countered.
An adjustable stand for a surgical microscope is described in U.S. Pat. No. 5,492,296. The adjustable stand includes first and second rotational joints. An elastic energy store is assigned to each one of these rotational joints. The elastic energy store includes a torsion spring having a pretension which can be adjusted. The elastic energy stores generate a compensating torque which counters a load torque in the rotational joints caused by the surgical microscope accommodated on the stand.
U.S. Pat. No. 5,667,186 discloses a holding arrangement for a medical-optical instrument wherein motorically-adjustable balancing weights are provided in order to compensate load torques occurring at the rotational axes of the holding arrangement.
U.S. Pat. No. 5,642,220 discloses a holding arrangement for a medical-optical instrument wherein a linear spring unit or a gas pressure cylinder is provided for generating a counter torque to compensate load torques. The linear spring unit or the gas pressure cylinder operate on a lever arm. A desired compensating torque can be adjusted in that a point of application of the gas pressure cylinder or linear spring unit is varied.
U.S. Pat. No. 5,402,582 discloses a holding arrangement for accommodating a probe head for measuring workpieces. The holding arrangement includes a multi-joint carrier arm. Torsion springs are provided in the joints of the carrier arm. These torsion springs generate torques which counter the load torques in these joints.
U.S. Pat. No. 5,332,181 discloses a motorized stand having a surgical microscope as a holding arrangement for a medical-optical instrument. This stand has a support column which is supported on a stand base and can be rotated about a vertical axis. A multi-joint carrier arm is arranged on this carrier column and has four rotational joints with motorized drives. A control unit is assigned to these motorized drives. The control unit is connected to angular transducers which are arranged on the rotational joints. The desired position of a specific rotational joint is inputted to the control unit. The drives of the holding arrangement are then supplied with current in correspondence to the pregiven joint position of a rotational joint in order to move a specific carrier arm section on a rotational joint into a desired angular position.
U.S. Pat. No. 6,471,165 discloses a surgical microscope having a stand which has a motorically-adjustable pivot axis running essentially horizontally. A step motor is disposed in this pivot axis. The step motor is controlled by an operator-controlled element and a servo adjustment of the surgical microscope, which is accommodated on this axis, is made possible. Force sensors or torque sensors are provided in the operator-controlled element.